Layered naturally occurring and synthetic smectites such as bentonite, montmorillonites and chlorites may be visualized as a "sandwich" composed of two outer layers of silicon tetrahedra and an inner layer of alumina octahedra. These "sandwiches" or platelets are stacked one upon the other to yield a clay particle. Normally this arrangement yields a repeated structure about every nine and one-half angstroms. A considerable amount of study has shown that these platelets can be separated further, by as much as 30 to 40 .ANG., i.e. interlayered by intercalation of various polar molecules such as water, ethylene glycol, and various amines. The solvent interlayered clays thus far prepared from naturally occurring smectites, however, are not suitable for general adsorbent and catalytic applications because they tend to collapse when subjected to high temperature.
In the past, clay materials have been intercalated with a variety of materials in order to form a supported open structure material which is useful as an adsorbent, a catalyst support, filtration medium or the like. However, it has been difficult to obtain a modified clay material which is stable at relatively high temperatures on the order of 250.degree. C.-500.degree. C. When a solvent swollen clay is heated to high temperature, the solvent is vaporized and collapse of the silicate sheets of the clay results as the solvent is removed from the interlamellar regions. This collapse significantly reduces the surface area of the clay because the internal surfaces are no longer available for adsorption. To solve this problem, a number of approaches have been taken to modify the clay by introducing supports or "columns" of material into the interlamellar regions of the clay to hold the silicate sheets of the clay apart. For instance, in the preparation of clay materials intended for use at relatively low to moderate temperatures, the clay layers have been separated with an organic material. For instance Shabtai et al. Proc. 6th Int. Congr. Catal., B5, 1-7 (1976) show a system in which smectite is interacted with di-or polycations derived from rigid, preferably cage-like amines, which acquire a single stable orientation in the interlayer space because of the steric requirements dictated by the configuration of the structure. A 1,4-diazabicyclo[2.2.2]octane-montmorillonite was found to possess significant molecular sieve properties and markedly higher catalytic activity for esterification of carboxylic acids in comparison to ordinary alkylammonium-exchanged montmorillonites.
The kaolin group materials comprise a silica tetrahedral sheet and an alumina octahedral sheet combined into the kaolin unit layer. Seto et al U.S. Pat. No. 4,159,994 show the intercalation of kaolin materials with an ammonium salt of a carboxylic acid having more than two carbon atoms, the alkali metal salt of a carboxylic acid having more than two carbon atoms, a lower alkylene glycol or a quaternized ammonium radical.
Because of the failure of the organic material impregnated clays at high temperatures, approaches have been taken to improve the stability of intercalated clays at high temperatures by intercalating clay substrates with various inorganic compounds, such as, for example, compounds of aluminum, bismuth, chromium, nickel, niobium, magnesium, silicon, tantalum and zirconium. Early work was carried out using aluminum chlorhydroxide as a pillaring agent. For example, see U.S. Pat. No. 4,176,090 issued Nov. 27, 1979 to Vaughan et al. Shabtai (U.S. Pat. No. 4,216,188 issued Aug. 5, 1980) uses colloidal solutions of metal hydroxides (sols) dispersed in the form of low molecular weight oligomers of polymers of aluminum or chromium hydroxides as pillaring agents. In Raible (U.S. Pat. No. 3,676,367 issued July 11, 1972) montmorin minerals are suspended in silicate solutions and subsequently free silica in precipitated between the layers of the montmorin mineral. More recent work has concentrated on using complexed ionic silicon as a pillaring agent. See, for example, the work of Pinnavaia et al, U.S. Pat. No. 4,376,163 issued Jan. 4, 1983.
Consistent among all the inorganic intercalated materials reported in the literature is a limited range of layer separations. Layer separation refers to the distance between facing clay surfaces on each side of the pillar (d.sub.1 in FIG. 1). These materials exhibit a layer separation ranging from about 3 to about 9 angstroms. The aluminum-containing pillars are at the upper end of the range and the silicon pillars are at the lower end of the range. The instant invention extends the range of layer separation distances obtainable using inorganic pillaring materials. Large layer separation distances allow the use of higher molecular weight and bulkier organic molecules to take part in catalytic reactions and adsorption processes.